1. Field of the Invention
This invention relates to a Ni--Zn base ferrite, and especially to a Ni--Zn base ferrite which is small in dielectric loss and high in saturation magnetization and is useful as a magnetic material in high-frequency fields.
Ni--Zn base ferrites are expected to find utility in many fields, for example, as core materials for screw cores, radios and other household electric appliances, high-frequency core materials, and magnetic materials for isolators, circulators and other high-frequency band products all of which make use of gyromagnetic effect. They are also examples of representative ferrite materials which are employed in devices such as circulators for microwave communication.
As a magnetic material usable for such application purposes, it is essential to select a material having a saturation magnetization (4.pi.Ms) of from 500 to 5,000 (gauss) and a small ferromagnetic resonance absorption half-value width (.DELTA.H) and, from the standpoint of assurance of reliability, a small dielectric loss tan .delta.(.epsilon.)!.
2. Description of the Related Art
The history of ferrites goes back many years. Developed as hard ferrites include Co-base ferrites, Ba-base ferrites, and Sr-base ferrites. As soft ferrites, on the other hand, Mg-base ferrites, Cu-base ferrites, Zn-base ferrites, Ni--Zn base ferrites and the like have been developed, followed by the development of Mn-Zn base ferrites.
Mg-base ferrites still remain as Mn-Mg-Zn base ferrites, which make use of rectangular hysteresis characteristics of the Mg-base ferrites and are used primarily in television sets (as deflection cores and flyback cores).
Concerning Cu-base ferrites, attempts were made at the time of their development to use them as memory elements in large scale computers. They were however accompanied by the problem that their structure at 1,000.degree. C. or higher had to be retained at room temperature. There was then a move toward the mass production of very small cores. As analog memory elements, they soon confronted their limitations.
Around that time, ICs, LSIs and the like were developed. A trend toward digital memories became a mainstream, and with this the era of analog memory elements came to an end.
Subsequent to the discovery of magnetic properties of Ni--Zn ferrites over a low frequency to high frequency range and their gyromagnetic effect, systematic and extensive research was conducted on them. They however had large magnetic losses. A great deal of efforts was hence concentrated on the improvement of their magnetic losses, but this problem has remained unresolved.
Ni--Zn ferrites offer the superior qualities as described above and specifically, they feature excellent magnetic properties over a low frequency to high frequency range, a small ferromagnetic resonance absorption half-value width AH, gyromagnetic effect, mild and flexible production conditions, and superior property reproducibility and stability. It is therefore clear that they will be used as primary magnetic materials in high-frequency fields once their dielectric losses tan .delta.(.epsilon.) are improved.
Conventional Ni--Zn ferrites have dielectric losses tan .delta.(.epsilon.) as large as 1.times.10.sup.-2 or so, thereby making their application in magnetic devices difficult.